Rev-limiter on Chinese "Happy Time" 80cc?

[Skyliner70cc]

Max speed won't hurt a thing provided the bearings can take it. With a bushing engine, I never had a problem going full throttle down a steep hill and running full throttle ALL day long.

You gotta give these HT engines a break, they aren't that bad. There is no reason why you couldn't run it at speeds as high as 8,000 rpm. The newer engines are much smoother and better balances than the older ones. I've got 2 stroke engines that are in the 25-50 cc range that I prop (they are on model airplanes) to spin 8500-9000 rpm at max throttle.

 

[HERPER]

my engine, an 80cc ht motor, when i go to my girlfriends house, its about a 10 mile ride and the whole time if not majority of the time is going about 20 or 22 mph. the max ive gotten is 30, and it didnt seem to be hurting too bad. maybe adjusting your throttle and ratio and mix could make your engine run better.

and def check all your parts before and after

 

[Ozi]

After about 27mph the engine acts like it is being controlled or held back by some kind of restrictive device.

If you have only done 100 miles

I could be wrong but I think Its called 'not run in yet' mine did the same

at about 150-180 mi that bogging down at wot dissapeared.

Ozi

 

[MMedlen]

I just got a response from Powerking and they indicate that their 80cc kit actually measures 69.3cc. This may be of help to those of you needing the info to get a good fit on a boost bottle.

 

[Ghost0]

Just a little background on these engines. The 50cc engines since they are smaller have been timed to produce good horse power over 6K rpm. The larger 70cc engines were designed to provide more torque so are timed to produce best power at a lower rpm. The "rev limiting" effect you are feeling is due to the port timing. The port timing on the 50cc is designed to Rev higher and the 70cc to rev lower. So your options are to change the port timing or to use the higher torque of the stock 70cc engine by gearing it taller.

 

[MMedlen]

Thanks for the info, I was not aware of the timing differences and that will be useful!

 

[fetor56]

100 miles is not enough as a run-in period to gain consistency in these engines.....see how u go after atleast 200 miles.

 

[try1897]

Hi, I went from a kings 70 / 80 cc to a Dax 65 and installed a 36 tooth . the 65 has less hp but it hums right along at 25 and purs like a kitten. runs sweet. It will do 30 or better but I don't want to blow it up so I tend to keep it down to 25 and cruse. It's gone a long way .Many many many miles and still sounds good idels well runs smooth and has had no knock on wood problems so far. Its going on a year and loving life.. T

 

[wildemere]

A 26" wheel at 30mph needs 7000rpm when using a 44t sprocket

6000rpm is 25.7 mph

 

[arceeguy]

VTBikeman analyzed the CDI unit and found that it will produce spark up to about 30,000 RPM - so there is no rev limiter built into the CDI.

Most of these engines now have roller bearings at both rod ends, and while this is mostly a good thing, it does make the engine less tolerant to over-revving. Once you hit the limit, the cage that holds the rollers breaks from the pounding and metal pieces start circulating through the crankcase. Bits of metal get caught in the transfer and exhaust ports and everything slows to a grinding halt. A bushing engine can be revved higher for longer without this type of failure, but the bushings are not particularly long lived in a two stroke because of the scant lubrication provided by the fuel/oil mix. The roller bearings need much less lubrication to survive.